The reduction of bisulfite to sulfide, as catalyzed by Desulfovibrio vulgaris and Desulfotomaculum nigrificans, will be investigated. The intermediates occurring during this process are trithionate and thiosulfate. An enzyme(s) which reduces trithionate to thiosulfate is composed of two separate protein fractions. We plan to purify these components and elucidate the role of each during thrithionate reduction. The role of membranes during the overall process of bisulfite reduction will also be studied. Preliminary data indicated that membranes were essential for the rapid reduction of bisulfite to sulfide.